In helicopter blades, it is common practice to utilize a trailing edge tab extending in the span direction of the helicopter blade and toward its outboard end for a selected distance and to permanently deform this trailing edge tab, also called the trim tab, selectively to alter the aerodynamic characteristics of an individual blade for the purpose of matching its performance to a master blade. The tab is deformed to an angle which will aerodynamically correct for imperfections which occur during the fabrication of the blade, that is, imperfections such as camber, and contour deviations. Once all the blades are "tracked" or match the master blade, the vibration levels in a helicopter rotor are minimized.
In the early prior art, a simple tool was used to bend the trailing edge tab. This tool had a trough shaped member which enveloped a small portion of the span dimension of the tab, and also had a handle projecting therefrom. Sections of the tab were manually bent by the operator applying force to the extending handle and thereby bending a portion of the blade tab. The next portion of the blade tab then had to be bent. Each successive portion so bent had to be separately measured to determine the degree of bending.
At a later time, more sophisticated tools, such as that taught in Roberts U.S. Pat. No. 2,422,042, were utilized. While the Roberts tool provided both means to bend the trailing edge tab and to measure the degree of bending, it grips the very trailing edge of the tab in a V-shaped notch so that it does not have the capability of bending the tab about a selected spanwise extending axis of the tab. In modern helicopter rotor trailing edge tabs, it is important to be able to bend the tab about a selected spanwise extending axis to avoid bending the tab at welds, and other joints that might be vulnerable to cracking. Further, the Roberts tool does not have the capability of measuring the true degree of bending simultaneously with the bending operation since the weight and friction of the bending apparatus is continually imposed upon the tab during both the bending and measuring operation. Therefore, the Roberts tool had to be removed to permit true bending measurements of the tab to be made.
At a later time, German Patent No. 2,358,205 to Messerschmidt Bolk taught a trailing edge tab bending and measuring apparatus but, as best understood, the apparatus does not have the capability of bending the trailing edge tab about a selected spanwise axis, nor obtaining the true degree of bending by eliminating the weight of the bending and measuring apparatus by appropriate counter weighting.